Simple Low Voltage Tube Preamp? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th January 2007, 05:42 PM   #1
CarlosT is offline CarlosT  United States
diyAudio Member
 
Join Date: Oct 2006
Default Simple Low Voltage Tube Preamp?

Have never done anything with tubes but I am intrigued about the "sound" of tubes. I was thinking about a simple tube pre-amp to an LM3875 chipamp.

I came across this low-voltage tube 512AX

CK512AX

Pinout: 1(red dot)=anode, 2=screen, 3=filament, 4=g1, 5=filament Vf=0.625V, If=20mA. Va max=45V, Vsg=45V. No power limitation, since you can't draw enough current to do anything bad.

Pentode mode: gm=160uS. Triode mode:gm=250uS, Ra=35k, MU=9.

Reasonable amplifier bias points:

Pentode: 0.7V bias. Va=22.5V, Vsg=27V, Anode supply=45V. anode resistor=180k. Ia=.12mA, Isg=.06mA.

Triode: 0.6V bias. Va+sg=22.5V, Anode supply=45V, load resistor=100k, Ia+sg=.2mA.

Could this be simply implemented with 25V transformers? Are there other simple miniature or low-voltage tubes that would sound good? Since this would be a preamp, a lotta gain is not important or even preferred.

Thanks!
  Reply With Quote
Old 30th January 2007, 06:12 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Steve Bench designed and built a battery powered pre-amp based on low voltage sub mini tubes. I think your proposal will work ok with 25V transformers. Another good low voltage candidate incidentally is the 6GM8.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 30th January 2007, 07:18 PM   #3
Jaime is offline Jaime  Uruguay
diyAudio Member
 
Jaime's Avatar
 
Join Date: Apr 2004
Location: Montevideo
Wavelength Audio (Gordon Rankin) made an expensive preamplifier with the 6GM8 tube. I think is a good option.

http://www.wavelengthaudio.com/preamps.html

best regards Jaime
__________________
I write in English worse than Tarzan
  Reply With Quote
Old 30th January 2007, 08:16 PM   #4
MRupp is offline MRupp  Germany
diyAudio Member
 
MRupp's Avatar
 
Join Date: Dec 2003
Location: Frankfurt area
Default Low Voltage Aikido preamp

OK, maybe not quite as simple, but you can build an Aikido preamp with the 6GM8 / ECC86, B+ voltage can be as low as 24V: http://www.tubecad.com/2006/04/blog0059.htm

As a benefit you can get superb PCBs from John Broskie at a reasonable price.
__________________
Martin Rupp
  Reply With Quote
Old 31st January 2007, 08:40 AM   #5
diyAudio Member
 
Join Date: Feb 2006
Location: Malaysia
Hi CarlosT,
What is your intention of the tube pre? do you need some gain or just a tube buffer?

Ecc88, 6922 can do at fairly low plate voltage of about 90V, low enough Rp to give low enough Zo, with a suitable plate choke, I think you can use ~100V B+ for the whole stage.

6AS7 or 6080 can also work in the 40~60 B+ zone... cathode follower if you must have that super low output mpedence, even with normal ground cathode, the impedance would still low enough for most applications.

6GM8 is good candidate, but From my experiments, I think the current is too small to produce good sounding cathode follower... I've not tried other method...

Cheers
__________________
Audio_Idiot
  Reply With Quote
Old 31st January 2007, 09:57 PM   #6
CarlosT is offline CarlosT  United States
diyAudio Member
 
Join Date: Oct 2006
WOW! So much to learn...so little time

That Aikido stuff was cool...as was the blog.

I got a buncha 25V + 25V toroidal trannies around so that's why I was thinking about low voltage tubes. I also currently have a combined channel mono LM3875 design which coulda benefitted from a buffer.
  Reply With Quote
Old 31st January 2007, 10:22 PM   #7
diyAudio Member
 
Join Date: Jan 2006
Location: Fairmount, GA
Dang you guys! This stuff is SOOO tempting!

Could someone elaborate on the two outputs of the Aikido pre? Could a similar circuit be used with just one tube per channel?

A schematic for mm phono also would be great.

Thinking about building one as a gift to my brother in law.

Thanks!
__________________
Poor stereo mix? Switch to mono! Perfect.
  Reply With Quote
Old 31st January 2007, 11:06 PM   #8
diyAudio Member
 
Join Date: Jan 2006
Location: Fairmount, GA
Oops! Just realized you need 2 tubes to total 24v for the filaments.
__________________
Poor stereo mix? Switch to mono! Perfect.
  Reply With Quote
Old 1st February 2007, 12:21 AM   #9
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally posted by davidlzimmer
Dang you guys! This stuff is SOOO tempting!

Could someone elaborate on the two outputs of the Aikido pre? Could a similar circuit be used with just one tube per channel?

A schematic for mm phono also would be great.

Thinking about building one as a gift to my brother in law.

Thanks!
Not one tube per channel, but you can use a single section on the input side - so three dual triodes total for two channels.

http://www.tubecad.com/2004/blog0013.htm

Sheldon
  Reply With Quote
Old 1st February 2007, 01:32 AM   #10
diyAudio Member
 
Join Date: Jan 2006
Location: Fairmount, GA
Sheldon,

Thanks, but I was wanting to stick with the 6GM8.

More importantly, the amp doesn't really need a pre. But an RIAA pre would be sweet!
__________________
Poor stereo mix? Switch to mono! Perfect.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low Voltage Tube Solidstate Guitar preamp design ... Minion Instruments and Amps 12 23rd April 2009 05:06 PM
Simple tube preamp? picklgreen Tubes / Valves 10 11th February 2007 11:11 AM
The most simple tube preamp timos_t Tubes / Valves 19 20th May 2006 06:23 AM
Newbie want to build simple tube preamp&psu!need help! thomgun_lc Tubes / Valves 55 29th November 2005 02:08 PM
Simple tube preamp... chrille Tubes / Valves 8 18th February 2003 09:44 PM


New To Site? Need Help?

All times are GMT. The time now is 09:51 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2